The present invention relates generally to induction heating and particularly to an induction heating apparatus which comprises a cycloconverter including a pair of inversely parallel connected gate-controlled switching devices.
In U.S. Pat. No. 3,821,509 issued to the same assignee as the present invention, there is described a solid state power converter which includes a gate controlled unidirectional switching device and a feedback diode inversely parallel connected to the switching device, and a resonant or commutating circuit connected in parallel with the switching device. The resonant circuit includes an induction heating coil and a capacitor which are tuned to a high frequency of the order of 20 kHz. A full-wave rectifier supplies rectified, unfiltered unidirectional voltage to the power converter. A gating circuit is provided to drive the switching device directly from the rectified unidirectional voltage. Upon gating of the switching device, the charge stored on the capacitor will be oscillated through the gated switching device and through the induction heating coil to reversely charge the capacitor. Upon reversal of the polarity, the switching device is turned off and a reverse current will flow through the feedback diode and through the induction heating coil to return the capacitor to the original charge minus any losses due to loading.
However, a comparatively greater number of components used in the known power converter with the consequential increase in cost and a greater loss of power due to inefficient operation have prevented the widespread use of induction heating apparatus for household applications.